The present invention relates to systems and processes for separating liquids of different densities. More specifically, the invention relates to a process and system for regenerating a liquid catalyst mixture utilized in the alkylation of olefin hydrocarbons by isoparaffin hydrocarbons.
The process of separating liquids in a separator having fractionation trays is well known in the art. One problem that can arise from the use of such a separator for separating liquids is the accumulation, and trapping, of an upper liquid phase above a lower liquid phase in the bottom of the separator. The upper liquid phase can become hydraulically trapped in the downcomer of the bottom tray, and/or trapped above the lower liquid phase in the bottom of the separator. This can cause flooding of the lower fractionation trays as the upper liquid phase backs up out of the downcomer and onto the lower fractionation trays, which detrimentally affects the separator operation.
A specific example of this is in the regeneration of a liquid catalyst mixture comprising hydrofluoric acid (HF), light acid soluble oil (ASO) and heavy ASO utilized in the alkylation of olefin hydrocarbons by isoparaffin hydrocarbons. The catalyst mixture is typically charged to a regeneration column, having fractionation trays, to contact an upwardly moving isoparaffin stream which strips HF out of the catalyst mixture for removal overhead. The remaining catalyst mixture accumulates in the bottom of the column wherein it separates into an upper phase (light ASO) above a lower phase (heavy ASO). The heavy ASO is removed out of the bottom of the column, but, the light ASO can become hydraulically trapped above the lower phase in the bottom of the separator and/or in the downcomer of the bottom fractionation tray. As the light ASO accumulates, the lower fractionation trays can flood, causing less efficient regeneration of the catalyst mixture. Thus, it is desirable to have a method and system for separating liquids, and more particularly, regenerating an alkylation unit catalyst mixture, in a more efficient manner and without flooding of the separator.
It is an object of the present invention to provide a system to be used in the separation of liquids in a more efficient manner.
It is a further object of the present invention to provide a method of separating liquids in a more efficient manner.
It is another object of the present invention to provide a method of separating liquids in a more efficient manner which includes a control system for controlling the level of an upper phase liquid forming in the bottom of the separator, above a lower phase liquid, to avert flooding of the separator with the upper phase liquid.
It is yet another object of the present invention to improve HF alkylation unit catalyst regeneration column operations.
In accordance with a first embodiment of the present invention, the separator includes:
a closed vessel having an inside wall, an upper portion, a lower portion, and an intermediate portion disposed between the lower portion and the upper portion, the lower portion of the closed vessel having an opening in the inside wall;
at least one fractionation tray disposed within the intermediate portion of the closed vessel, the at least one fractionation tray including a bottom tray having an upper surface;
a first conduit extending through and downwardly from the bottom tray into the lower portion of the closed vessel and connecting the lower portion of the closed vessel and the intermediate portion of the closed vessel in fluid flow communication, the first conduit having a longitudinal axis, an inner surface, an open top end spatially located above the upper surface of the bottom tray, an open bottom end spatially located below the bottom tray and an opening in the inner surface intermediate the open top end and the open bottom end; and
a second conduit having a longitudinal axis, an open first end, an open second end spatially located below the open first end, and an outside surface, the open first end of the second conduit disposed within the first conduit, wherein the open first end of the second conduit opens generally in the direction of and below the open top end of the first conduit, the open second end of the second conduit extends through the opening in the inner surface of the first conduit and the open second end of the second conduit further extends through the opening in the inside wall of the lower portion of the closed vessel, the outside surface of the open second end of the second conduit being in sealing engagement with the opening in the inner surface of the first conduit, and the outside surface of the open second end of the second conduit being in sealing engagement with the opening in the inside wall of the lower portion of the closed vessel.
In accordance with a second embodiment of the present invention, the separator described in the first embodiment further comprises:
a third conduit operably related to the intermediate portion of the closed vessel;
a fourth conduit operably related to the upper portion of the closed vessel; and
a fifth conduit operably related to the lower portion of the closed vessel.
In accordance with a third embodiment of the present invention, the separator described in the second embodiment further comprises:
a sixth conduit operably related to the lower portion of the closed vessel.
In accordance with a fourth embodiment of the present invention, a preferred method of operating the separator described above in the second embodiment includes:
introducing an inlet liquid stream comprising a first liquid component, a second liquid component and a third liquid component into the intermediate portion of the closed vessel and above the bottom tray via the third conduit;
withdrawing at least a portion of the first liquid component from the upper portion of the closed vessel via the fourth conduit;
accumulating at least a portion of the second liquid component and at least a portion of the third liquid component in the lower portion of the closed vessel;
allowing the at least a portion of the second liquid component and the at least a portion of the third liquid component to undergo a gravity phase separation to thereby produce a top phase comprising the at least a portion of the second liquid component and a bottom phase comprising the at least a portion of the third liquid component;
withdrawing at least a portion of the top phase from the lower portion of the closed vessel via the second conduit; and
withdrawing at least a portion of the bottom phase from the lower portion of the closed vessel via the fifth conduit.
In accordance with a fifth embodiment of the present invention, a preferred method of operating the separator described in the third embodiment includes:
introducing an HF catalyst into the intermediate portion of the closed vessel and above the bottom tray through the third conduit;
introducing a vaporous isoparaffin stripping fluid into the lower portion of the closed vessel and below the bottom tray through the sixth conduit;
withdrawing an overhead stream comprising HF and the vaporous isoparaffin stripping fluid from the upper portion of the closed vessel through the fourth conduit;
accumulating the light ASO and the heavy ASO in the lower portion of the closed vessel;
allowing the light ASO and the heavy ASO to undergo a gravity phase separation, in the lower portion of the closed vessel, to thereby produce a top phase comprising the light ASO and a bottom phase comprising the heavy ASO;
withdrawing at least a portion of the top phase from the lower portion of the closed vessel through the second conduit; and
withdrawing at least a portion of the bottom phase from the lower portion of the closed vessel through the fifth conduit.
In accordance with a sixth embodiment of the present invention, the process and/or system of the present invention as described in the fifth embodiment further comprises a control system for indirectly maintaining the level of liquid in the first conduit at or near a predetermined level.
Other objects and advantages of the invention will be apparent from the detailed description of the invention and the appended claims.